Two-dimensional model of elastically coupled molecular motors

A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed.     

Simple and universal method in designs of high-efficiency diffractive optical elements for spectrum separation and beam concentration

Diffractive optical elements(DOEs) with spectrum separation and beam concentration(SSBC) functions have important applications in solar cell systems. With the SSBC DOEs, the sunlight radiation is divided into several wave bands so as to be effectively absorbed by photovoltaic materials with different band gaps. A new method is proposed for designing high-efficiency SSBC DOEs, which is physically simple, numerically fast, and universally applicable. The SSBC DOEs are designed by the new design method, and their performances are analyzed by the Fresnel diffraction integral method.The new design method takes two advantages over the previous design method. Firstly, the optical focusing efficiency is heightened by up to 10%. Secondly, focal positions of all the designed wavelengths can be designated arbitrarily and independently. It is believed that the designed SSBC DOEs should have practical applications to solar cell systems.     

顶端ZnO纳米结构对GaN基LED光提取效率的影响

为了提高GaN基蓝光LED的光提取效率,本文建立了LED顶面分别铺设ZnO纳米柱和纳米锥结构的两种模型,利用时域有限差分法对两种模型进行仿真并对结果进行了比较.仿真结果表明,ZnO纳米结构的各项几何结构参量(包括排列周期P、高度L、宽度W以及斜率k等),对LED顶端光提取效率影响显著.仿真分别得到了两种结构的最佳模型,通过比较,LED顶面纳米柱和纳米锥结构对光提取效率的提高效果相近,其最佳提取效率分别增强至无任何结构时的2.5倍和2.3倍.同时,通过对各项参量扫描获得的对光提取效率的变化曲线进行了分析,并给出了相应相应的理论解释.这些模型优化和理论分析对实际的高性能GaN基LED的设计制造有着指导意义.     

高辐射效率超宽谱脉冲辐射天线的设计与实验

设计了一种采用共面TEM馈电结构的抛物反射面超宽谱脉冲辐射天线,分析了该种馈电结构的阻抗特性与辐射特性。实验表明当馈入电压为3kV、前沿180ps的超宽谱脉冲时,该天线主轴辐射场测试距离与峰值场强之积平均值达到18.3kV,相较于常用的TEM喇叭馈电的超宽带反射面天线,其辐射效率有了显著的提高。     

光子回声量子存储器中非均匀展宽频谱对存储效率的影响

本文提出了一个利用光子回声技术探究非均匀展宽频谱线形(如高斯、洛伦兹分布)对存储效率影响的简捷方法。我们发现当信号光脉冲的持续时间与介质频谱线宽的乘积远大于1时,可将分布函数的傅里叶变换近似成狄拉克函数,使得研究非均匀展宽频谱对存储效率的影响变得非常容易;通过计算发现不同线形分布达到最佳存储效率的光学深度有所不同,频谱线形趋于均匀时达到最优存储效率的存储介质光学深度最小。该研究对实验上实现最优化光量子态存储具有指导意义。     

全光纤模式转换器的设计及优化

提出了一种新型全光纤LP02模宽带模式转换器.基于模式匹配原理采用双芯光纤设计,利用LP11模作为中间过渡模式,实现了宽带模式转换.运用光束传播法和模式耦合理论分析了光纤参量对有效折射率的影响,选择合适的光纤参量实现了模式匹配,分析了纤芯距离等参量对模式转换效率和带宽的影响,对比相同光纤参量下,直接和间接模式转换方法,数值模拟表明,采用间接法能够有效提高模式转换带宽,当要求转换效率大于80%时,这种模式转换器带宽能够达到121nm.     

F8BT：P3HT共混薄膜的放大自发辐射

研究了聚合物poly（9,9-dioctylfluorene-co-benzothiadiazole）（F8BT）和poly （3-hexylthiophene）（P3HT）共混薄膜的放大自发辐射（ASE）现象,对影响其阈值的两个因素--增益和损耗进行了详细的研究。结果显示,共混聚合物的发光效率随着P3HT所占比例的增加有所降低。当P3HT比例低于20%时,发光效率降低不多,而其损耗则随着P3HT的增加显著减小。F8BT和P3HT混合后,光损耗系数从7.8 cm^-1下降到4 cm^-1左右。这表明F8BT：P3HT共混聚合物光波导的ASE阈值降低主要是由于其损耗的降低而导致的。ASE阈值的降低预示该材料体系容易实现电泵浦激光。     

换热器的综合效率分析

利用分析的方法对换热器进行了性能分析,推导出了综合评价换热器性能的公式;并以芳烃生产工艺中制苯工段的换热器为实例进行了具体的效率分析,得出了换热器的效率、单位面积的收益、损失及综合性能评价指标。结果表明:流体发生相变的换热器的性能要优于单相流体换热器的性能。     

Improved efficiency droop characteristics in an InGaN/GaN light-emitting diode with a novel designed last barrier structure

<正>In this study,the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically.The energy band diagrams,electrostatic field near the last quantum barrier,carrier concentration in the quantum well,internal quantum efficiency,and light output power are systematically investigated.The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction.These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.     

Is the US stock market becoming weakly efficient over time? Evidence from 80-year-long data

We propose a degree of market efficiency in terms of entropy concepts. The relative efficiency for the US stock market varies over time from 1929 to 2012, with a slight decline in the past 10 years.